Field of the Invention
The present invention relates to a dynamically cured blend of a grafted elastomeric polyolefin copolymer and a thermoplastic crystalline polyolefin.
European Patent Application No. 0014018 discloses grafted elastomeric polyolefin copolymer which optionally may be blended with another polymer such as polyethylene, polyamides or vinyl polymers. No curatives are added. In the examples the preferred blending polymer is polypropylene which has been grafted with maleic acid at the same time the elastomeric copolymer is grafted with maleic acid. Such compositions are not very useful as thermoplastic elastomers due to their poor resistance to compression set.
Thermoplastic elastomer compositions consisting of blends of polyolefin resin and cured EPDM elastomer are known, U.S. Patent No. 4,130,535. Such blends have a number of limitations due to the curatives used to crosslink the EPDM elastomer. Free-radical curing system initiated by high-energy radiation or by peroxides tend to crosslink polyethylene when it is the polyolefin resin resulting in impaired thermoplastic processability and tend to degrade polypropylene resin when it is the polyolefin resulting in a reduction of the strength of the composition. Sulfur vulcanization systems exhibit unpleasant odors, bloom, and provide compositions with less than optimal resistance to oil swell and compression set. It is disclosed in U.S. Pat. 4,311,628 that the above shortcomings can be overcome by the use of phenolic curatives to crosslink the EPDM component of the blends. Such compositions require the use of metal oxides and halides as cure promoters. The presence of metal derivatives can result in less than optimal water resistance and can contribute to poor electrical properties particularly poor wet electrical properties. None of the above inventions are effective for preparing thermoplastic compositions of noncrosslinked polyolefin resin and crosslinked EPM rubber. It has now beendiscovered that improved thermoplastic compositions of noncrosslinked polyolefin resin and crosslinked EPDM or EPM elastomer can be prepared by using grafted EPDM or EPM as the elastomer and employing diamines or polyamines as the curatives to crosslink the elastomer.